The UNSC Marine Corps is a branch of the United Nations Space Command's Armed Forces responsible for conducting land-based expeditionary combat operations, using the mobility provided by the UNSC Navy to rapidly deliver forces. Marines are also charged with the defense of Navy vessels and installations from hostile forces. While structured under the Unified Ground Command,[5] the UNSC Marine Corps operates closely with the UNSC Naval Command and has some authority within the office.[6] The Marine Corps is one of the five branches of the UNSC Armed Forces.[7]

The decisive success of this campaign had a major impact on future military doctrine, resulting in UNSC Navy warships carrying large Marine contingents for ground assaults and boarding actions. Following the success of the UNSC Marine Corps at Mars, recruitment drives and propaganda tactics strongly bolstered UNSC forces and the Koslovics and Friedens were defeated on Earth in 2170.[10]

In 2524, a Marine battalion was posted at the colony world of Tribute, commanded by Lieutenant Colonel Aboim and supported by the corvette UNSC Bum Rush, with air support from AV-14 Hornets. The battalion attempted to put a stop to rebel bomb makers near the city of Casbah. Two special warfare squads, led by Staff SergeantsAvery Johnson and Nolan Byrne, were involved in disastrous operation in June. Byrne's team was killed during a hostage situation at a Jim Dandy restaurant near Casbah city; thirty-eight civilians, three Marines, and two rebels were killed in the bombing.[12]

Not long after the First Battle of Harvest, the Corps' experienced one of their first major encounters with the Covenant at numerous engagements throughout the Outer Colonies, including the Harvest Campaign, eventually lasting from 2526 to 2531. At the final stages of the campaign, the Marines quickly established a base of operations in Harvest's arctic region. A reconnaissance force led by SergeantJohn Forge was deployed to survey the area. However, during the patrol, Covenant forces under the command of ArbiterRipa 'Moramee overran and nearly destroyed the base. Forge rallied scattered marines, who quickly retook it from the aliens. After receiving reinforcements and repairing the base, the Marines fought through a sizable Covenant garrison force in an attempt to secure a mysterious Forerunnerstructure in the region.

The Battle of Arcadia saw the UNSC Marine Corps holding the defensive line around major population centers to allow evacuation for the civilian population with the assistance of the SPARTAN-II Red Team. Successfully keeping Covenant forces from occupying the population centers, the Corps' began launching multiple assaults on the Covenant's base of operations to reclaim the planet.

The UNSC Marine Corps would take part in numerous actions against the Covenant on many of the Outer Colonies in the years that followed. Unfortunately, they were hopelessly outgunned, out-numbered and out-flanked by the Covenant forces and the Marine Corps would suffer tremendous losses in what eventually saw the near-destruction of the Outer Colonies.

The Corps' experienced another encounter with the Covenant on the colony world of Sigma Octanus IV in 2552. Upon landing, the Marines' hardware and equipments were rendered useless due to the planet's harsh environment. In the first stage of the battle, during a naval engagement, a Covenant DDS-class carrier was able to land a large contingent of troops on the northern pole of the planet. The Covenant were able to take Côte d'Azur, a major population center. Fortunately almost all of the civilian population was evacuated beforehand, but the UNSC Marine Corps' GeneralKits launched a failed assault to retake the city.

The UNSC Marine Corps maintained a sizable presence on Reach when the Covenant stormed the planet; they bypassed the defense fleet in orbit, as well as the MAC Gun platforms, and made a considerable landing of soldiers on the North and South Poles. During the early hours of the battle, the Covenant had overrun FLEETCOM HQ on Reach, destroying the perimeter and swarming the Marine defenders with Banshees, Wraiths, and battalions of infantry. The situation became severe and critical when the Marines were forced to defend the Orbital Defense Generators against a massive Covenant assault, using every available armored vehicle and defensive position from available bunkers. The Battle of Reach became one of the most devastating defeats for the UNSC Marine Corps in the Human-Covenant War.

The surviving Marines from the Battle of Reach served an important role in the Battle of Installation 04, taking part in such engagements as securing the UNSC Pillar of Autumn crash site, launching multiple guerrilla assaults on Covenant convoys and base of operations and rescuing captured Pillar of Autumn's personnel from a Covenant battlecruiser. Initially, the Marines were part of a special operation consisting of a sizable Orbital Drop Shock Trooper special forces detachment and a standard Marine detachment to infiltrate Covenant High Command and kidnap a Covenant Prophet.

Several Marine detachments achieved a turning point during the course of the Battle of Earth when they managed to retake the cities and maintain temporary ground control for UNSC reinforcements to arrive. One such Marine detachment was E2-BAG/1/7, which was able to engage the Covenant ground forces in Mombasa, Kenya as the Covenant assault carrier landed ground forces in the city.

The Marine Corps also partook in a major assault alongside the UNSC Navy in the Battle of Voi. As ground forces, the Marines were to engage in the Battle of Voi with a SPARTAN-II supersoldier by eliminating anti-air vehicles and batteries, as well as destroying temporary Covenant outposts to allow UNSC reinforcements to refortify the area.

The Marines fought in the war's last battle at the Ark. Starting with their deployment in an operation codenamed Operation: BLIND FAITH,[13] the Marines launched numerous attacks on Brute strongholds, including an attack on the Ark's cartographer. After fighting on foot, and in heavy vehicles, the Marines drove off the Covenant. They then teamed up with the Elites and attacked three barrier towers protecting the Ark's Citadel. After capturing the first tower, with the help of the Master Chief, Marines and UNSC pilots then defeated the Covenant aerial forces. They then waited for the deactivation of the third tower, where they then staged an attack on the Citadel. After fighting two Scarabs, they were then evacuated back to the fleet while the Master Chief and the Arbiter killed Truth. The surviving Marine forces fell back to Earth through the Portal onboard the Shadow of Intent before Installation 08 was activated.

In addition to conventional forces, the Marine Corps maintain special operations forces in the form of the Orbital Drop Shock Troopers. ODSTs drop into hostile areas via SOEIVs prior to the main invasion. They attempt to complete some of the most difficult tasks in hostile areas, such as clearing enemy ground forces or establishing landing zones for incoming Pelicans.[20][23]

Large numbers of men and women are employed by the UNSC Marine Corps. Service people hold ranks, which are divided between officers and enlisted. The rank structure of the UNSC Marine Corps is based around that of the United States Marine Corps.

Marine Corps Dress Uniforms are worn on formal or ceremonial occasions, and are similar to those worn by their 20th and 21st Century predecessors in the United States Marine Corps. A variety of dress uniforms exist, including a white-and-blue uniform,[24] an all-blue uniform,[25] and an all-black funerary uniform.[26]

In the field, Marines usually wear passively camouflaged uniforms with usually green M52B body armor. Lightweight, though durable, the armor is surprisingly resilient. Marines don Ushuaia Armory's CH252 helmets equipped with a heads-up display and radio system.[27] These helmets are mounted with recorders,[28] and certain models feature holographic text-displaying eyepieces or ballistic goggles. In addition to helmets, Marines on field operations in more humid locales sometimes choose to wear boonie covers, or those in colder environments don visored and thicker helmets. Marine NCOs are easily recognized by the cover they wear complete with the UNSC insignia, although they oftentimes substitute this soft cover for a more practical protective helmet; post-war NCOs often wear a variant with a fully sealed helmet that is otherwise worn by scouts. Marines sometimes don small helmet communications microphones or black-phased sunglasses on their helmets, and others carry backpacks. Marines sometimes wear black gloves to protect their hands and improve their grip on their weapons. Some Marines sport orange visors which attach to the brim of their helmets. Marines operating in cold environments wear environmentally-tailored armor, with insulated snow camouflage utilities and full body armor as well as insulated and visored helmets with something analogous to a balaclava.[29] Marines also wear the lightweight and protective VZG7 armored boots, the standard footwear of the Marine Corps since the middle of the 26th century.[27]

Orbital Drop Shock Troopers sport heavy and articulated black battle armor, which also double as an armored g-suit that allows for safe transport in small ships during turbulent atmospheric entry. They also wear fully-visored, black helmets that cover the entirety of the head, and can withstand several headshots. This armor, overall, provides ODSTs with more protection than standard marine armor.

Less standard vehicles also saw service with the Marine Corps during the Human-Covenant War. The M-145D Rhino was outfitted with a reverse-engineered plasma mortar. The Gremlin Combat Support Vehicle is used to disable enemy vehicles with its onboard EMP weapon. The Cyclops support exoskeleton was used both repair duties and logistical support, as well as in combat, though it was eventually retired from service. In recent years, the Mantis has been utilized by the Marines, with the Corps having contracted Materials Group to produce a refit package to allow alternate loadouts on the walker.[49]

The Marine Corps' most common aircraft is the Pelican dropship. The Pelican is used as a multirole aerodyne which is capable of carrying numerous armament configurations, including Scorpion anti-tank missiles, Anvil II air-to-surface missiles, as well as a chin-mounted 7.62mm machine gun, or a 40mm or 70mm autocannon. The Pelican can also be outfitted with an M247 or AIE-486H machine gun in its troop bay.

The UNSC Marine Corps operates the GA-TL1 Longsword as its primary fighter/interceptor and as a tactical bomber. The Corps also operates the Shortsword-class Bomber, which serves as a close air support aircraft. The Marines utilize the AV-14 Hornet as a light attack craft and gunship. Earlier in the war, the Marines also utilized the AV-22 Sparrowhawk as a close air support gunship, though it was largely retired from service due to problems with its propulsion system. Currently, the AV-49 Wasp supplements the Marine Corps' existing stocks of AV-14 and AV-22 aircraft.[50] Heavy air-to-ground support is provided by the AC-220 Vulture gunship. Marine air units are usually intended to support ground forces or to drop off vital equipment for the Marines, either in close-air-support or air interdiction roles, with the UNSC Navy and the UNSC Air Force taking on the dedicated air force role.[51]

Marines are a playable unit in Halo Wars that can be built from a Barracks for 100 resources and one population slot. Armed with MA5B assault rifles and have the ability to throw M9 frag grenades. Marines are a jack of all trades, master of none-type unit typically used to counter aircraft. Marines have the following upgrades:

New Blood: Adds another Marine to the squad. Costs 200 resources and a tech level of 1.

Medic: Adds a Medic to the Marine squad allowing the unit to heal itself after battle. Costs 700 resources and a tech level of 3.

ODST: Turns all Marines into ODSTs (only available if Captain Cutter is the leader). Armed with M90 shotguns, ODSTs are able to be dropped in from drop pods. Costs 1800 resources and a tech level of 3.

Marines can be built by all UNSC leaders at the Firebase. They are a jack-of-all trades unit, performing adequately against infantry, vehicles, aircraft, and structures. Marines can no longer upgraded to ODSTs, who are now a distinct unit that can only be called via Leader Power. In Blitz Marines cost 20 energy, Extractor Marines cost 50 energy, Reactive Marines cost 50 energy, and Armored Marines cost 60 energy.

The UNSC Marine Corps shares many traits of its culture and organization with the modern United States Marine Corps. Like the USMC, the UNSCMC organizes its units into divisions, which are subdivided into regiments. Most other military forces of the present day are subdivided into brigades. In addition, every known UNSCMC rank corresponds directly to a USMC rank, and the enlisted and officer ranks that have been described imply that the exact same insignia are used as well. Semper Fi, the Latin motto used by the USMC, short for Semper Fidelis ("Always Faithful" or "Forever Faithful") is also used by the UNSCMC.[52] "Ooh Rah", a motivational call originating from the USMC, is often said by Marines of the UNSCMC.

In the Halo: Combat Evolved level The Truth and Reconciliation, Captain Keyes tells a Marine to "Stow your bellyaching, soldier - remember, you're a leatherneck!" Leatherneck was a nickname earned by US Marines in the era of the Continental Marines. The Marines would wear leather collars to provide protection from slashing attacks as they boarded enemy ships. Although an appropriate reference to Marines, the term "Leatherneck" and "soldier" are viewed by their respective service members as being incompatible, and a means of differentiating between service in the Marine Corps or Army.

The equipment and armor used by UNSC Marines (particularly in Halo: Combat Evolved, resembles those used by the US Colonial Marines in the 1986 film Aliens, one of many similarities to the film in the Halo series. The Marines' equipment also bears some resemblance to the US Army's Future Force Warrior program. They also bear a striking resemblance look to the soldiers in Starship Troopers.